Re: [PATCH v3 2/2] riscv: topology: fix default topology reporting

[Sudeep Holla]

On Sat, Jul 09, 2022 at 04:23:55PM +0100, Conor Dooley wrote:
> From: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> 
> RISC-V has no sane defaults to fall back on where there is no cpu-map
> in the devicetree.
> Without sane defaults, the package, core and thread IDs are all set to
> -1. This causes user-visible inaccuracies for tools like hwloc/lstopo
> which rely on the sysfs cpu topology files to detect a system's
> topology.
> 
> On a PolarFire SoC, which should have 4 harts with a thread each,
> lstopo currently reports:
> 
> Machine (793MB total)
>   Package L#0
>     NUMANode L#0 (P#0 793MB)
>     Core L#0
>       L1d L#0 (32KB) + L1i L#0 (32KB) + PU L#0 (P#0)
>       L1d L#1 (32KB) + L1i L#1 (32KB) + PU L#1 (P#1)
>       L1d L#2 (32KB) + L1i L#2 (32KB) + PU L#2 (P#2)
>       L1d L#3 (32KB) + L1i L#3 (32KB) + PU L#3 (P#3)
> 
> Adding calls to store_cpu_topology() in {boot,smp} hart bringup code
> results in the correct topolgy being reported:
> 
> Machine (793MB total)
>   Package L#0
>     NUMANode L#0 (P#0 793MB)
>     L1d L#0 (32KB) + L1i L#0 (32KB) + Core L#0 + PU L#0 (P#0)
>     L1d L#1 (32KB) + L1i L#1 (32KB) + Core L#1 + PU L#1 (P#1)
>     L1d L#2 (32KB) + L1i L#2 (32KB) + Core L#2 + PU L#2 (P#2)
>     L1d L#3 (32KB) + L1i L#3 (32KB) + Core L#3 + PU L#3 (P#3)
> 
> CC: stable@xxxxxxxxxxxxxxx
> Fixes: 03f11f03dbfe ("RISC-V: Parse cpu topology during boot.")
> Reported-by: Brice Goglin <Brice.Goglin@xxxxxxxx>
> Link: https://github.com/open-mpi/hwloc/issues/536
> Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> ---
> ---
>  arch/riscv/Kconfig          | 2 +-
>  arch/riscv/kernel/smpboot.c | 4 +++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 2af0701b7518..4b6c2fdbb57c 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -52,7 +52,7 @@ config RISCV
>  	select COMMON_CLK
>  	select CPU_PM if CPU_IDLE
>  	select EDAC_SUPPORT
> -	select GENERIC_ARCH_TOPOLOGY if SMP
> +	select GENERIC_ARCH_TOPOLOGY

I am not sure of !SMP as ARM64 is default SMP only. I have never reviewed
the arch topology code with !SMP considered. I will leave that part to
RISC-V developers.

>  	select GENERIC_ATOMIC64 if !64BIT
>  	select GENERIC_CLOCKEVENTS_BROADCAST if SMP
>  	select GENERIC_EARLY_IOREMAP
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index f1e4948a4b52..a1c861f84fe2 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -40,6 +40,8 @@ static DECLARE_COMPLETION(cpu_running);
>  void __init smp_prepare_boot_cpu(void)
>  {
>  	init_cpu_topology();
> +
> +	store_cpu_topology(smp_processor_id());
>  }
>  
>  void __init smp_prepare_cpus(unsigned int max_cpus)
> @@ -161,9 +163,9 @@ asmlinkage __visible void smp_callin(void)
>  	mmgrab(mm);
>  	current->active_mm = mm;
>  
> +	store_cpu_topology(curr_cpuid);
>  	notify_cpu_starting(curr_cpuid);
>  	numa_add_cpu(curr_cpuid);
> -	update_siblings_masks(curr_cpuid);
>  	set_cpu_online(curr_cpuid, 1);
>  
>  	/*

Other than that, this looks good. FWIW:
Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx>

-- 
Regards,
Sudeep